Recently, by converting electronic book data to speech waveforms using a speech synthesis system, a method for listening the electronic book data as an audio book is proposed. In this method, an arbitrary document can be converted to speech waveforms, and a user can enjoy the electronic book data by reading speech.
In order to support reading of a document by speech waveform, a method for automatically assigning an utterance style used for converting a text to a speech waveform is proposed. For example, by referring to a feeling dictionary defining correspondence between words and feeling, a kind of feeling (joy, anger, and so on) and a level thereof are assigned to each word included in a sentence of a reading target. By counting the assignment result in the sentence, an utterance style of the sentence is estimated.
However, in this technique, word information extracted from a simple sentence is only used. Accordingly, relationship (context) between the simple sentence and sentences adjacent thereto is not taken into consideration.